Pressure medium actuated percussion mechanism



Jan. 13, 1970 A. NOREN 3,489,228

Filed Feb. 12, 1968 3 Sheets-Sheet 2 Pic-3.2 We 49 1.1 I I 2 I 8 I I 9 35 as 37 33 o o o five/775w:

' ARA/E A/mF/v Jan. 13, 1970 A. NOREN ,489,

PRESSURE MEDIUM ACTUATEDPERCUSSION MECHANISM v Filed Feb. 12, 1968 5 Sheets-Sheet 3 2: 1 g /'--26 V 21 I 1 A? 1.

United States Patent Us. c1. 173 75 17 Claims ABSTRACT OF THE DISCLOSURE A percussion tool having a cylinder with a drive piston at one end and a percussion piston at the other end, the cylinder being filled with a fluid to transmit the force of the driving piston to the percussion piston, and a valve sleeve slidable in the cylinder between the two pistons and slidable with the drive piston, the drive piston having vent passages sealingly engaged by the sleeve during the power stroke of the drive piston; a chamber communicating with said vent passages; the valve sleeve being driven more rapidly toward the percussion piston than the drive piston near the end of the driving portion of the power stroke to unseal the vent passages and allow venting of the space between the drive and percussion pistons near the end of the driving portions of the power stroke.

This invention relates to a pressure medium actuated percussion mechanism, preferably for use in reciprocating drilling machines in which at the end of a cylinder filled with a pressure medium, such as a gas or a liquid, a drive piston is mounted and adapted to be displaced in the cylinder by an outside power source and via the pressure medium to drive a percussion piston which is mounted at the other end of the cylinder or connected therewith to strike against a tool or the like.

In a known percussion mechanism of this type, as it is described in US. patent specification 3,140,586, a percussion piston portion acting as a valve is adapted to open one or several return passageways for the pressure medium, whereby the percussion piston during the later part of its working stroke is disconnected from the positive drive of the drive piston. The return passageways are exposed when the speed of the drive piston is at maximum before the drive piston has reached its turning position.

The percussion piston, after it has struck against the tool, returns at high speed into the cylinder, whereby the return passageway or passageways again are closed by that percussion piston portion which acts as a valve. The return force of the percussion piston also is obtained in that a vacuum is produced above the percussion piston side facing away from the tool, when the percussion piston is being pressed down. Upon the return movement of the percussion piston and the closing of the passageways, a strong overpressure is produced in the cylinder, thereby giving rise to great mechanical stresses and jerky operation. If the drive piston was not given the time for turning, the percussion piston when it meets the pressure medium flow from the drive piston on its down stroke, may return and thereby cause the pistons to operate nonequally.

For relieving the overpressure in the cylinder to some extent, according to the aforementioned patent specification a return passageway in the form of a groove is provided in the drive piston and cylinder wall. This measure, however, is not sufficient to eliminate the disadvantages of jerky operation etc. The return passageway formed by the groove has too small an area to enable it to effectively relieve the pressure. The most serious dis- 3,489,228 Patented Jan. 13, 1970 advantage, however, is the existence of great sealing problems. The drive piston, as a matter of fact, must be effectively sealed against the cylinder, because the smallest leakage would reduced the efiiciency degree of the percussion mechanism and thereby the resulting impact force against the tool. An effective sealing cannot be obtained when grooves are formed in the piston and cylinder.

The object of the invention, thus, is to eliminate said disadvantages of the known apparatus and to produce a percussion mechanism which operates smoothly and extremely jerk-free.

This object is achieved according to the invention in a percussion mechanism of the type described, in that the drive piston is provided with a valve sleeve which participates in the drive piston motion and is adapted to close return passageways for the pressure medium in the drive piston which communicates with a pressure medium chamber outside the cylinder, and that means are provided, so to move the valve sleeve in relation to the drive piston, when the drive piston during its working stroke is in a predetermined position, that said return passageways in said drive piston are exposed to the pressure medium chamber, thereby allowing the pressure medium to flow through the return passageways to the pressure medium chamber.

This construction offers the advantage over the known apparatus, that a great return area for the pressure medium is exposed as soon as the drive piston has reached maximum speed, with the object of ventilating the overpressure of the cylinder.

Leakage possibilities, moreover, are reduced to a minimum, because no grooves or the like for the pressure relief must bemade in parts movable in relation to each other, but, instead, use is made of a valve sleeve which is movable in relation to a seat, thereby rendering it possible to design a construction which is absolutely tight when the valve is in its closed position.

Additional advantages of the mechanism according to the invention will become evident from the following description in connection with the drawings.

FIG. 1 shows in a schematic way a principle outline through a percussion mechanism according to the invention, in a section.

FIG. 2 shows a view of a reciprocating drilling machine in which the mechanism according to the invention is applied, parts of the machine being shown in a section, so as to make details thereof apparent.

FIG. 3 shows on an enlarged scale a detail of the percussion mechanism in another embodiment.

FIG. 4 shows a section through the percussion mechanism along the line 4-4 in FIG. 3.

The percussion mechanism shown in FIG. 1 comprises a cylinder I inserted in a housing 2 which may constitute part of the casing in a reciprocating drilling machine (FIG. 2), in which the percussion mechanism according to the invention as applied. In the housing 2, as appearing from the aforesaid and enclosing the cylinder 1, measures are taken for receiving the pressure medium, for example a presure liquid, utilized for the operation of the reciprocating drilling mechanism. Very generally it can be said, that the space 212 above the cylinder 1 and the cylinder 1 proper are filled with pressure medium. In one end of the cylinder 1 drive piston 3 is mounted and actuated by an outside drive mechanism, which in the embodiment shown is an eccentric 4 mounted in the machine housing 2 by means of a shaft 5. Said eccentric 4 abuts that end of the drive piston 3 which faces away from the cylinder 1. The shaft 5 can be driven directly or indirectly, for example over a flywheel and a gear (not shown), by a drive means (drive engine) which is connected to the axle journal 6 (FIG. 2) of the shaft 5 or ear and projects out of the machine housing. The drive iston is loaded in the direction of the eccentric 4 by a ompression spring 7 mounted within the cylinder 1.

At that end of cylinder 1 which faces away from the rive piston 3, a percussion piston 8 is mounted in a perussion cylinder 9 which is an extension of the machine ousing 2. The percussion piston is provided with a pin projecting into the cylinder 1 and sealed in relation to he cylinder 1 by a sealing device 11. In the cylinder wall above the sealing device 11, one or several return pasageways 12 for the pressure liquid in the cylinder 1 are rovided and adapted to be opened and closed by the in 10 of the percussion piston. The return passageways 2 communicate with the pressure liquid chamber 2a by eturn ducts (not shown in detail).

The mechanism operates in such a manner, that the rive piston 3 is driven into the cylinder 1 by the eccenric 4, The pressure liquid enclosed in cylinder 1 thereby resses the percussion piston pin 10 out of the cylinder whereby the percussion piston is driven in the working lirection against a drilling tool 13, the end of which pro- :cts into the percussion cylinder 9. The pin 10 of the ercussion piston is smaller in' diameter than the drive neans, thereby imparting to the percussion piston a highr speed. In the moment approximate to that when the rive piston has reached maximum speed, the percussion viston 10 exposes the passageway or passageways 12, and he percussion piston continues to move in the working .irection free from actuation by the drive piston via the lressure liquid, which latter, instead, flows via the return vassageways 12 to the pressure medium chamber 2a. Vhen the percussion piston 8, at the position indicated 'y dash-dotted lines in FIG. 1, has struck against the lrilling tool 13 and been reversed, the pin 10, during the eturn motion, again closes the return passageways 12 and eturns into the cylinder. The return motion of the percusion piston is etfected both by the strike against the tool .3 and by the vacuum produced above the percussion iston 8 when it is being pressed down. Thus, no return pring for the percussion piston is required.

This drive mechanism substantially corresponds to that lescribed in US. patent specification 3,140,586, and it has he advantages in relation to a mechanical drive of the 'ercussion mechanism as stated in said patent specificaion.

The aforementioned diificulties in relieving the overpresure in cylinder 1 at a desired predetermined position now re eliminated, in that between the end 14 of the drive iston 3 projecting into the cylinder 1 and the cylinder 1 s mounted with limited movability a valve sleeve 15 sealng via sealing rings against the cylinder 1. The portion .6 of the drive piston 3 located above the valve sleeve 15 s provided with a step 17 having such a shape and angle hat it can abut against and form a sealed valve seat for corresponding surface 18 formed at the peripheral edge f the valve sleeve 15. The body of the drive piston 3 is rovided with fluid passages 19 which connect the cham- Ier 2a with passages 21, the passages being closed when he valve face 17 strikes against valve seat 18 during opertion of the machine. It is to be observed that the eccenric does not close the opening of the passageways 19 acing the eccentric, because the eccentric 4 has a curved urface, while the end of the drive piston 3 is plane. k stem portion 14 of the drive piston 3 extends into the 'alve sleeve 15 and has a cruciform cross section as shown .t 14 in FIGURE 4. The portion 16 of the drive piston ocated above the valve sleeve 15 is given a diameter less han the outer diameter of the sleeve 15, i.e. the inner liameter of the cylinder 1, so that between the drive )iston 3 and the cylinder 1 an annular chamber 22 is ormed above the valve sleeve 15. One end position of the 'alve sleeve 15 in the cylinder is defined by a stop ring :3 in the cylinder barrel 1.

The valve means described operates as follows. When he eccentric 4 presses down the drive piston, the step 17 )f the latter strikes against the surface 18 of the valve sleeve, and the return passageways 19 are closed. The valve sleeve 15 participates in the continued motion of the piston 3 into the cylinder 1, whereby the percussion piston 8 is actuated in the aforedescribed manner by the pressure liquid enclosed. When maximum speed has been reached and preferably at the same time as the pin 10 of the percussion piston 8 exposes the return passageways 12, according to the invention now the return passageways 19 in the drive piston 3 shall be opened, so that the pressure liquid can pass through these return passageways to the outside of the drive piston 3, i.e., to the pressure medium chamber 2a. The opening of these passageways is effected in that the drive piston 3 and the valve sleeve 15 positively are separated at a predetermined position.

This occurs in the preferred embodiment shown in FIG. 1 by the pressure medium. For this reason, the wall of the cylinder 1 adjacent the drive piston is spaced from said piston to form an annular chamber 22 therebetween and accommodates a sealing ring 24 formed on said piston 3, said ring having a sliding fit within the wall of the chamber 22. The distance between the end of the annular chamber 22, i.e. the end of cylinder 1, and the flange 24 corresponds to that part of the working stroke at which the return passageways 19 shall be closed, When at the predetermined position of piston 3 the flange 24 enters the annular chamber 22 and interrupts the connection of the latter with the pressure medium chamber 2a, upon the continued motion of the piston 3 into the cylinder 1 a pressure is built up on the liquid amout enclosed in the annular chamber 22, which pressure is transmitted to the surface 25 of the valve sleeve 15 exposed to the annular chamber 22. Said surface 25 is smaller than the surface of the flange 24, since the valve sleeve 15 has a smaller outer diameter than the flange 24, and both have the same defining diameter inwardly. Thus, the valve sleeve 15 is subjected to a greater pressure, i.e. it is given a higher speed than the drive piston 3, so that the sleeve is pressed away from the piston and a gap 26 is exposed. Then the pressure liquid can flow from cylinder 1 through the return passageways 21, the gap 26 and the return passageways 19. The movability of the valve sleeve 15 in relation to the drive piston 3 suitably can be limited in that a shoulder 27 in the sleeve strikes against the compression spring 7. Of course, also other stop means can be arranged.

In the embodiment shown in FIG. 3 the valve sleeve 15 is directly actuated mechanically by the drive mechanism, for example by means of a cam 28 on the valve sleeve, whichprojects all about the drive piston 3 and is guided directly by its abutment to the peripheral surface of the eccentric 4. The cam is of such shape that at the predetermined position the valve sleeve 15 is pressed into the cylinder more rapidly than the drive piston 3, so that the surface 17 on the drive piston and the surface 18 on the valve sleeve 15 are separated, and the gap 26 is exposed. Then the pressure liquid can flow out of cylinder 1 through the passageways 21 in the portion 14 of the drive piston 3 through the gap 26 and out into the chamber 2a. In this case, thus, the return passageways 19 and the flange 24 on the portion 16 of the drive piston 3 located outside the valve sleeve 15 are eliminated, so that the piston can be given a shorter length.

The percussion mechanism according to the invention, further, is provided with means, in the embodiment shown with a fan 30 mounted on the shaft 5 of the drive mechanism (FIG. 2), by which fan an overpressure is maintained in the cylinder 9 of the percussion piston 8, so that borings are prevented from penetrating into the percussion cylinder. The fan 30 sucks in air through an ilet 31 in the machine housing 2 and presses the air through a line 32 to an inlet 34 in the surface of the percussion cylinder 9, said inlet 34 being provided with a check valve 33 and having the form of inlet holes 35. In operations which do not involve the risk of borings, the overpressure can be ventilated via outlet holes 36 which normally are closed by a sealing 37, which easily can be moved aside when the overpressure is to be relieved.

During the drilling operation the drilling tool 13 must be rotated, at the same time as it is subjected to impacts by the percussion piston 8. This is eifected by a drive means which in the embodiment comprises a worm screw 40 driven from the drive mechanism of the machine in a manner not shown in detail. The worm screw 40 drives a pinion (not shown) mounted at one end of a shaft 41, the other end of which supports a pinion 42 meshing with a cog wheel 43 which is shaped on or secured to the drill chuck 44 in which the drilling tool 13 is mounted.

For preventing damage to the drive means, for example when the drill seizes, it is usual to provide some kind of shear means in the drive mechanism, for example shearing pins or the like. In order to eliminate the need of such means, for the exchange of which the drilling operation must be interrupted according to the invention the worm screw 40 is connected to the drive mechanism via a coupling, for example a fluid coupling 45. Couplings of another type, for example friction couplings, may also be used. At its end facing away from the coupling 45, the worm screw 40 is mounted displaceably, in the embodiment shown in such a way, that the worm shaft is displacea ble in a bearing 46 and pressed in the direction to the coupling 45 so that the coupling is maintained engaged, by means of a compression spring 47 which abuts the bearing at one end and at the other end presses the worm screw axially in the direction to the coupling.

When the drilling tool seizes while in operation, the increased moment will cause the screwing of the worm screw, against the action of compression spring 47, in the direction away from the coupling 45 to the spring, so that the directly or indirectly meshing parts of the coupling are separated, and the coupling is disengaged.

The moment at which the coupling 45 is disengaged, can be determined by a suitable choice of the compression spring 47. In the embodiment shown, the moment also can be re-adjusted, as desired, because the bearing 46 contacted by the compression spring is mounted in a sleeve 48 screwed into the machine housing. By screwing the sleeve 48 in or out with a lever 49, the bearing can be displaced in axial direction in relation to the coupling 45 and thereby increase or decrease the pressure from the compression spring 47.

The shown embodiment of the invention can be varied and modified without abandoning the object of the invention.

What I claimed is:

1. In a pressure medium actuated percussion mechanism adapted for use in reciprocating drilling machines, a casing including a cylinder at one end of the casing filled with a pressure medium, a drive piston in one end of the cylinder, a percussion piston in the other end of the casing mounted to strike against a tool or the like, a rotary eccentric drive means engaging said drive piston to drive it toward said percussion piston and to transfer driving force to said percussion piston via said pressure medium, a valve sleeve in the cylinder between the drive piston and the percussion piston which moves with the drive piston, said drive piston having vent passage means sealingly engaged by said valve sleeve during the driving portion of the power stroke of the drive piston, whereby the pressure medium is operatively retained in the space between the drive piston and the percussion piston during said driving portion, pressure medium vent chamber means outside the cylinder communicating with said vent passage means, and thrust-transmitting coupling means operatively related to said eccentric drive means and said valve sleeve, said coupling means including means to render said coupling means operative responsive to the approach of the rotary eccentric drive means to the end of its driving stroke to displace the valve sleeve more rapidly toward the percussion piston than the drive piston near the end of the driving portion of said power stroke, whereby to unseal said vent passage means and allow venting of the space between the drive piston and the percussion piston to said vent chamber means near the end of the driving portion of the power stroke.

2. The mechanism according to claim 1, characterized in that a stop ring is provided in the cylinder to limit the return stroke of the valve sleeve to a predetermined position.

3. A reciprocating drilling machine, characterized in that ilt is provided with a percussion mechanism according to claim 1.

4. The machine according to claim 3, characterized in that means operatively connected to the drive means of the percussion mechanism are provided for continuously supplying air to the space between the percussion piston and the tool, so that overpressure is produced in the percussion cylinder for preventing borings from penetrating into said cylinder.

5. The machine according to claim 4, characterized in that said last named means are a fan connected to the drive means of the percussion mechanism, and that the air is supplied to the working chamber through a line provided with a stop valve.

6. The machine according to claim 3, provided with means for imparting to the drilling tool chuck a rotary motion, characterized in that between the drive source and the drive means of the chuck a coupling is mounted which disengages at a certain predetermined amount of resistance.

7. The machine according to claim 6, characterized in that the last named coupling is a friction or fluid coupling having one engaging portion connected to the power source of the machine, the other engaging portion of the coupling being connected with a worm screw meshing with a worm gear mounted between the coupling and the tool chuck, in such a manner, that the worm screw is mounted displaceably against spring action, so as to yield in such a direction that the engaging portion of the coupling no longer are in drivingconnection with one another.

8. The machine according to claim 7, characterized in that the worm screw is mounted at one end displaceably in a bearing, and that between the worm screw and the bearing a compression spring or the like is mounted, said bearing preferably being adjustable for an optional setting of the spring pressure exerted on the worm screw.

9. The pressure medium actuated percussion mechanism of claim 1, and wherein the means to displace the valve sleeve more rapidly then the drive piston comprises cooperating sealing means on the drive piston and valve sleeve defining between the drive piston and the valve sleeve a sealed compression space containing pressure.

medium near the end of the driving portion of said power stroke.

10. The pressure medium actuated percussion mechanism of claim 9, and wherein the means defining said sealed compression space includes a portion of the cylinder.

11. The pressure medium actuated percussion mechanism of claim 10, and wherein said portion of the cylinder includes an enlarged bore portion at said one end of the cylinder.

12. The pressure medium actuated percussion mechanism of claim 11, and wherein said means defining said compression space includes a peripheral flange on the drive piston slidably and sealingly receivable in said enlarged bore portion.

13. The pressure medium actuated percussion mechanism of claim 12, and wherein said drive piston is provided with an annular step sealingly engageable with the peripheral edge of the valve sleeve, said vent passage means opening at said step.

14. The pressure medium actuated percussion mechanism of claim 13, including spring means operatively 'asaciated with said valve sleeve for biasing the valve sleeve ward the drive piston.

15. The pressure medium actuated percussion mechaism of claim 1, and wherein said drive means comprises rotary eccentric drivingly engaging the end of the drive iston to drive it toward the percussion piston.

16. The pressure medium actuated percussion mechaism of claim 15, and wherein the means to displace the alve sleeve more rapidly toward the percussion piston icludes cooperating cam means on the eccentric and the alve sleeve.

17. The pressure medium actuated percussion mechaism of claim 15, and wherein the means to displace the alve sleeve more rapidly toward the percussion piston inludes a cam on the valve abutting the peripheral surace of the eccentric and shaped so as to separate the valve sleeve from the vent passage means of the drive piston near the end of the driving portion of the power stroke of the drive piston.

References Cited UNITED STATES PATENTS NILES BYERS, JR., Primary Examiner US. Cl. X.R. 94 49 

